With the general public becoming more environmentally aware and the cost of energy sources increasing, recycling of various products has been steadily gaining favor with various industries. Certain products, such as glass and plastic containers, lend themselves to recycling because of their ability to maintain their physical integrity and their mechanical properties during their use. However, the initial cost of manufacturing these types of containers is high due to the cost of the raw materials and the complicated manufacturing processes necessary for forming them.
Vast quantities of paper products are consumed daily in modern society. However, due to the perishability of these paper products and the limited use that can be made of these paper products upon reclamation, extensive utilization of reclaimed paper products has not yet been realized. Although various processes are currently available for utilizing recycled paper in the form of pulp, molded products produced by these processes are limited in the complexity of their form and structure and do not offer satisfactory surface characteristics and physical properties.
U.S. Pat. No. 1 324 935 discloses a process for forming hollow articles, such as bottles, jars, cases, boxes and similar containers, tubes and like structures, from fibrous material held in suspension. In this reference, a fibrous material or pulp held in suspension in a liquid is deposited on a forming mold and then preliminarily dried before entering into a pressing step where the pulp is formed into a finished article. However, the process of this patent is limited to the production of simple, uncomplicated articles.
U.S. Pat. No. 2 023 200 shows a method for making molded pulp containers having smooth internal and external surfaces and optionally providing ribs either in the inner or outer surfaces of the container. The process of this reference also involves the separation of paper or wood pulp out of a solution and onto a forming mold and the preliminary drying of the pulp to a water content of between 45 to 55 percent by weight before a final compression state. Although the articles produced by the process disclosed in this reference can have crude detailing, such as ribs formed thereon, the provision of more sophisticated detailing, such as threads on the articles, is not possible.
U.S. Pat. No. 2 369 488 discloses a method of manufacturing hollow articles, such as a textile winding core or cone, out of paper pulp which have a core whose outer surface is of sufficient strength to withstand a thread being wound therearound. The paper pulp is mixed with a binder and, optionally, other additives before being deposited on a rotating former to form an embryo cone. The embryo cone is then subjected to a preliminary compacting step to reduce the water content thereof and then to compacting, densifying and shaping operations. Although this reference discloses the manufacture of a hollow article out of paper pulp which is capable of supporting a thread wound on the surface thereof, it is necessary that a binder and, optionally, other additives be added to the paper pulp in order to provide a paper article having the physical properties necessary for the desired purposes.
U.S. Pat. No. 2 986 490 discloses a method for making molded pup articles in which wet molded articles having a moisture content varying from about 10 percent to 75 percent are subjected to a drying and finishing operation between a set of complemental heated pressing dies. However, this method is incapable of producing molded paper products having the improved physical characteristics of the present invention.
U.S. Pat. No. 4 491 502 discloses a method of making a molded paper container, such as a dish or tray, from a paperboard sheet in which a formed sheet is dried to a water content in the range of from about 50 to about 100 percent by weight and then subjected to pressing and drying in a matched metal die set. Although the molded paperboard product of this method is said to have improved strength characteristics, the process of this patent is incapable of producing paper articles having complex configurations.
Therefore, an important object of the present invention is to provide a method capable of producing a molded paper pulp article having an improved surface appearance and superior mechanical and physical properties.
A further object is to provide a relatively simple and inexpensive method for forming a molded paper pulp article having improved surface characteristics, improved mechanical properties and which can be formed into complex structures and recycled.